β-fructofuranosidases are enzymes that recognize and hydrolyze fructose in a carbohydrate containing a terminal fructose residue. Some β-fructofuranosidases have a fructose transfer activity transferring the fructose formed by hydrolysis to a substrate, as well as the hydrolysis activity. Those β-fructofuranosidases can form a trisaccharide kestose in which one molecule of glucose is bonded to two molecules of fructose using sucrose as a substrate.
Among such kestoses, 1-kestose is known as a useful oligosaccharide, for example, because it retains sweetness similar to sucrose (sugar) and has approximately half of the calorie of sugar while offering approximately ⅓ of the sweetness of sugar, rarely increases blood glucose levels when ingested, and exhibits antiallergic functions (Patent Literature 1). For example, a β-fructofuranosidase derived from Aspergillus niger and a β-fructofuranosidase variant containing an amino acid mutation in the amino acid sequence thereof are disclosed (Patent Literature 2 and 3) as β-fructofuranosidases that form 1-kestose.